Fastener Testing Services: What’s Covered & How to Choose a Lab
Magnetic system of non-destructive quality control. Check the quality of the welded joint of steel pipes.Fasteners — bolts, nuts, screws, rivets, washers, pins, and studs — are the connectors that hold engineered systems together. Despite their apparent simplicity, fasteners are safety-critical components whose failure can trigger catastrophic consequences — from structural collapses to vehicle accidents. Fastener testing is the systematic quality assurance process that verifies these components meet their mechanical, chemical, dimensional, and performance requirements before they are installed in critical applications.
Why Is Fastener Testing Important?
Fastener testing is crucial in various industries to prevent product failures, accidents, and costly repairs. It ensures that fasteners meet industry standards and perform their intended functions safely and reliably, contributing to quality control and product assurance. The consequences of fastener failure extend far beyond the cost of a single replacement part — a single under-strength bolt in a structural joint or a brittle fastener susceptible to hydrogen embrittlement can trigger failures with severe safety and liability consequences.
Fastener testing is beneficial for: evaluating materials during selection and qualification, ensuring the continued quality and reliability of purchased or manufactured products, and detecting in-service issues through periodic sampling programs.
Core Fastener Testing Methods
Tensile Strength Testing
The fundamental mechanical test for fasteners measures ultimate tensile strength (UTS), yield strength (or proof load), and elongation. Two configurations are defined:
Axial tensile test: The fastener is loaded along its central axis, and the maximum tensile load it can sustain before fracture is measured. Results confirm compliance with the minimum tensile strength requirement of the applicable fastener property class (SAE Grade, ISO property class, or ASTM designation).
Wedge tensile test: A wedge is placed under the fastener head before applying axial load, creating combined tensile and bending stress. This test is required for hex head, socket head cap screws, and square head fasteners — confirming that the fastener can withstand the bending moment that arises during tightening and loading in a real joint. ASTM F606/F606M governs both test methods.
Proof Load Testing
A specified proof load (a defined fraction of minimum UTS) is applied to the fastener for a defined dwell time. The fastener must sustain the proof load without fracturing or permanently elongating beyond the specified tolerance. This test directly verifies that the fastener will not permanently deform at its specified maximum installation preload.
Shear Strength Testing
Shear testing evaluates the fastener’s resistance to forces applied parallel to its axis — the governing failure mode for fasteners in lap joints, pin connections, and clevis assemblies. The maximum shear load is measured and compared against the specified minimum shear strength.
Hardness Testing
Rockwell hardness testing (typically HRC or HRB, depending on the fastener grade and material) verifies both minimum hardness (ensuring adequate strength) and maximum hardness (preventing susceptibility to hydrogen embrittlement in high-strength grades). NACE MR0175/ISO 15156 specifies hardness limits for sour service applications.
Torque-Tension Testing
This test establishes the relationship between applied installation torque and the resulting clamping tension (preload). Knowing the torque coefficient (K-factor or nut factor) for a specific fastener/surface combination enables accurate specification of the installation torque to achieve the target preload, which is critical for both proper joint function and the prevention of fatigue failures from under-preload and material damage from over-preload.
Chemical Composition Analysis
OES, XRF, or ICP analysis confirms that the fastener material meets the specified alloy composition. Material grade substitution — using a lower-grade alloy that appears dimensionally identical — is a documented failure mode in fastener quality incidents, particularly for imported fasteners.
Plating and Coating Evaluation
XRF or metallographic cross-section measurement verifies that protective plating (zinc, cadmium, nickel, zinc-nickel) meets minimum thickness requirements. Hydrogen embrittlement testing after plating (slow-strain-rate or sustained-load tests) verifies that the plating process has not introduced damaging hydrogen into the fastener material.
Salt Spray Corrosion Testing (ASTM B117)
Salt spray testing evaluates the fastener’s corrosion protection over the specified exposure duration — confirming that the plating or coating will provide adequate protection in the intended service environment.
Dimensional Inspection
Comprehensive dimensional inspection verifies thread pitch, thread form (profile), major and minor diameters, head dimensions, grip length, and overall fastener length against the dimensional requirements of ASME B18, DIN, ISO, or customer drawing specifications. Non-conforming dimensions cause fit-up failures, cross-threading, and joint geometry problems.
Fatigue Testing
Fatigue testing subjects fasteners to cyclic axial loading at defined stress levels, characterizing their fatigue strength for applications involving dynamic loads or vibration — a critical requirement for automotive, aerospace, and industrial applications, where fasteners experience millions of load cycles in service.
Fastener Testing Standards
Key standards governing fastener testing include:
- ASTM F606/F606M — Mechanical Properties Testing of Externally and Internally Threaded Fasteners
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners (inch series)
- ISO 898-1 — Mechanical Properties of Fasteners — Bolts, Screws and Studs (metric)
- ASME B18 — Dimensional standards for various fastener types
- ASTM B117 — Salt spray corrosion testing
- NACE MR0175/ISO 15156 — Hardness limits and testing for sour service
Industries Requiring Fastener Testing
Aerospace and Defense: Safety-critical fasteners in airframes, engine mounts, and landing gear require certification to NAS, MS, or MIL-SPEC standards. Infinita Lab works with defense and government agencies, providing testing and certification for Tier I and Tier II suppliers.
Automotive: Tensile, fatigue, torque-tension, and salt spray testing are specified for fasteners in powertrain, chassis, suspension, and body structure applications per SAE and OEM requirements.
Industrial Equipment: Pressure vessels, piping flanges, rotating machinery, and structural connections use fasteners that require proof load, tensile, and corrosion qualification.
Electronics: Precision screws and threaded inserts in electronic equipment require verification of dimensions, hardness, and torque-tension.
Conclusion
Fastener testing is essential to ensure the mechanical integrity, material quality, and performance reliability of safety-critical components used across industries. By applying standardized tests such as tensile, proof load, hardness, corrosion, and fatigue evaluations, manufacturers can verify compliance, prevent catastrophic failures, and maintain consistent product quality. A comprehensive testing program not only safeguards structural and operational reliability but also reduces risk, liability, and long-term costs associated with fastener failure.
Infinita Lab’s Fastener Testing Services
Infinita Lab provides comprehensive fastener testing — tensile (axial and wedge), proof load, shear, hardness, torque-tension, chemical composition, plating, salt spray, and fatigue — through its nationwide network of accredited partner laboratories. Testing complies with ASTM F606, SAE J429, ISO 898, and other applicable standards, with certified test reports.
Contact Infinita Lab: (888) 878-3090 | www.infinitalab.com
Frequently Asked Questions (FAQs)
What is fastener testing and why is it necessary? Fastener testing is the systematic quality assurance process verifying that fasteners meet mechanical, chemical, dimensional, and corrosion performance requirements — preventing failures in the joints and structures they secure, which can have serious safety and economic consequences.
What is the wedge tensile test for fasteners and why is it more demanding than the axial test? The wedge tensile test places a wedge under the fastener head before applying tensile load, creating combined tensile and bending stress. This is more demanding than pure axial loading because it replicates the bending moment a fastener experiences when a joint is imperfectly aligned during installation or loading.
What ASTM standard governs mechanical testing of fasteners? ASTM F606/F606M — Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets — is the primary US standard.
What is torque-tension testing and why does it matter for fastener installation? Torque-tension testing measures the relationship between applied torque and resulting clamping preload for a specific fastener/surface combination. This allows engineers to specify the installation torque that achieves the target preload — critical for joint function, fatigue life, and prevention of loosening or overtorque damage.
What is hydrogen embrittlement testing and which fasteners require it? Hydrogen embrittlement testing verifies that high-strength steel fasteners have not been embrittled by hydrogen introduced during electroplating. It is typically required for fasteners with hardness above ~HRC 32–35 (approximately 1000 MPa tensile strength) that have been electroplated. Tests include slow strain rate or sustained load tests after plating to detect delayed fracture susceptibility.
